The present invention relates to key-operated locks, for any kind of doors, windows or openings wherein a bolt is needed to lock and keep closed a door or the like. Particularly, the invention relates to a lock of the kind comprising a key-operated bolt, movable between a resting position and a locking position and which is retained in each of these positions by one or more gated security levers or bolt-retaining sliders, either of the pivoted or sliding type, the sliders being required to be lifted by the key before the latter can operate the bolt. The invention particularly refers to the provision of a bolt-locking arrangement that is arranged to hold or retain the bolt in the locking-extended position. The lock of the invention is also a combination changing lock because the combination of the lock may be changed by simply using a key different to the one last used to open the lock. Thus, the lock of the present invention may be operated by two or more different keys.
Conventional locks comprise bolts which are slidably movably arranged within a lock box or case which in turn is located in, for example, a door to lock and keep the door closed against the frame or a wall opening. To move the bolt, between a locking extended position and a resting retracted position, a key is necessary having a bit with a plurality of steps, each step being intended to operate against one or more notches of the bolt. In order to keep the bolt locked in position, either in locking or in resting position, a plurality of security gated levers or bolt-retaining sliders are provided. The bolt usually has a stump extending transversely thereof and projecting from a side thereof. Each slider, in turn, has a window, gate, or a locking slot and the bolt stump extends through these slots. When the sliders are in a resting position, the locking slots retain the stump causing the bolt to be held against movement. When the sliders are lifted by the key steps, the locking slots become aligned so as to release the bolt stump whereby the bolt may be moved by at least one step of the key that engages the notches of the bolt. Thus, with the bolt released, the lock may be opened or locked.
The bolt retaining sliders are constantly biased by resilient means, such as a spring, towards the position is wherein the bolt stump is retained by the locking slots. Once the key has been rotated to slidably move the bolt, either to open it or to shut it, the key is removed from the lock whereby the bolt retaining sliders move downwardly to the resting position, under the action of the spring, and the bolt stump is retained by the locking slots of the sliders. The sliders also have notches to be operated, that is lifted, by the key steps. The different shapes of the sliders' notches and of the locking slots, as well as the different heights of the key steps are what is called the secrecy of the lock.
To guarantee the secrecy of the lock and avoid the possibility that any unauthorized person may open a lock, the quantity of sliders and consequently the number of the key steps have been increased. In this manner, the quantity of combinations of the lock have been considerably increased and the probabilities of lock violation have been thus reduced.
Conventionally, the quantity of sliders have increased from one or two sliders to more than four sliders and, recently, locks having eight sliders are in use.
Brazilian Patent application number MU 5,901,257, published on Jan. 29, 1980, refers to a lock having two dependent commands operating with two keys. Although the security of this lock is increased regarding other locks, the operation of this lock is complex and cumbersome.
U.K. patent No. 1,128,461 refers to improvements in key operated locks, the improvements being suitable for a suite of locks each operable individually by its own key, known as a single key, or by one or more master keys which may comprise the grand master, for a whole suite, or also a sub-master, for part of a suite.
U.K. patent No. 757,446 refers to lever locks for doors, wherein the key-operated bolt is detained in each of one of its extreme positions by one or more gated security levers, of either the pivoted or sliding type, which levers require to be lifted by the key before the latter can operate the bolt and the invention is particularly concerned with differing and master-keying as applied to this kind of lock.
U.K. patent No. 944,354 refers to an improved key controlled combination changing, permutation lock, particularly suitable for lockers and the like. The lock comprises a lock bolt movement controlling mechanism and a plurality of tumbler discs operativelly connected with said block bolt movement controlling mechanism, a turnable unitary dial and knob extending exteriorly of one side of the casing of the lock and operatively connected with the tumbler disc, a clutch plate included in said connections for transmittal rotation from the knob to the tumbler discs according to a preselected combination, the knob being provided to move the clutch plate for combination changing proposes while a key is also required.
Argentine patent No. 159,469 refers to an improved lock characterized in that the combination sliders are not biased by any kind of spring while they retract to the resting position under the gravity force when the key is removed from the lock.
Swiss patent Nrs. 472,563 and 588,001 refer to locks wherein a lever is actuated together with a locking element to close the lock. When the lever is moved said locking element is released.
The above cited prior art does not overcome the problem of modifying the combination of the lock unless the shape of the sliders' notches are modified together with the steps of the key bit. This requires removal of the lock from the door and opening of the lock box to modify the sliders by removing material thereof.
The question of the secrecy of a lock is a very important problem that has not been solved. Although a lock may be very complex and sophisticated, an unauthorized person may have access to the keys of the lock and may obtain copies thereof to then open the lock. This may lead to serious consequences when a key is stolen and copied with intention of violating a house to rob, kidnap or commit any kind of crime. There are criminal gangs that pay rich families' maids for keys that have been stolen from the family in order to then break into the house.
Conventionally, the keys are operated by turning them about two or more rounds, however, in an attempt to overcome the above problems it is quite usual to use an extra key in order to provide a further rotation with a different secrecy. Although this allows the user to have control on the keys of the lock, the use of a second key is cumbersome, and the problem is not entirely solved.